Piston



June 18, 1946.

0. L. STARR PISTON r 2 Sheets-Sheet 1 Original Filed July 8, 1940INVENTOR. 05662 L. STA/2E M/mfiy ATTORNEY.

June 18 1946. o. STARR 2,402,213

PISTON Original Filed July 8, 1940 2 Sheets-Sheet 2 INVENTOR. 056/912 L-.STHEE ATTORNEY Patented June 18, 1946 PISTON Oscar L. Starr, MissionSan Jose, Calii.'., assignor to Caterpillar Tractor (10., San Leandro,CaliL, a corporation of California Original application July 8, 1940,Serial No.

Divided and this application November 12, 1943, Serial No. 509,961

4 Claims. 1

and also wear of the ring in its seating groove.

The present application is a division of my copending application,Serial No. 344,304 for Piston, filed July 8, 1940, which issued on May'30. 1944, and became Patent No. 2,349.91'7.

In manypistons, particularly those adapted for compression ignitionengines (Diesel engines) of the type having an auxiliary combustionchamber, such as a precombust'ion chamber, the "top or crown of thepiston is frequently formed with a combustion crater which provides partof the main combustion chamber of the engine. tlally ignited fuel andhot air from the auxiliary combustion chamber pass into such craterduring the combustion phase; and due to completion of combustion in thecrater, it becomes hotter than the remainder of the piston crown. Inorder to provide for equal distribution of heat from the combustioncrater to the perlphery'of the piston and thereby obviate distortion ofthe crown which results in the piston rings and their seating groovesbecoming distorted or m'isalined with respect to the cylinder wall,thereby adversely affecting sealing relationship of such rings in theirseating grooves and with the cylinder wall, it is desirable that thecrater be disposed in the crown concentric with the axis of the piston.

However, this necessitates placing, the auxiliary combustion chamberdirectly over the axis of the Piston which if done, does not providesuificient room in the head of the engine, for proper positioning of theintake and exhaust valves. and adequate cooling water jacket spacetherefor. Consequently, to provide ample room for the valves andsumcient cooling jacket space in the head of the engine, the auxiliarycombustion chamber is generally inclined and offset to one side withrespect to the axis of the piston and this requires that the combustioncrater in the crown of the piston be eccentrically disposed or offsetwith respect to the axis of the piston.

Heretofore, with such offset combustion crater,

Par-- rings are mounted, commonly designated as the ring belt portion ofthe piston; and because of the difference in temperature in suchperipheral parts, the ring belt portion and the crown of the pistonwould warp or how unequally. As a result, the top compression ring andits seating groove. because they are nearest the crown, and sometimesother rings and their seating grooves, if the warping were bad, eventhough in proper alinement with respect to the cylinder wall and inproper sealing relationship when the piston was cold, would be moved outof proper sealing relationship with respect to each other and out ofalinement with respect to the cylinder wall when the piston was hot; anda poor seal of the ring in its groove and with the cylinder, wall wouldresult, causing loss of compression or blow-by.

Another problem in connection with efficient sealing of a piston ringwith the cylinder-wall. and also in the seating groove therefor, resultsfrom the fact that for dissipating heat rapidly from the piston, whichis particularly desirable in compression ignition engines because theyopcrate under relatively high maximum temperatures. it is advantageousto have the piston of metal, such as aluminum, which has relatively highheat conductivity. Also, a metal such as peripheral part of the pistonclosest to the crater to become hotter than'the'opposite peripheral partcithe piston. Such parts are in the'peripheral -portion of the piston inwhich the piston aluminum, possesses the additional advantage ofimparting lightness to the piston. Aluminum is relatively soft comparedto cast iron, especially at operating temperatures of a piston crown;the latter material being generally employed for piston rings. As aresult, when a piston ring is seated in a ring groove formed directlyinan aluminum piston body, it readily wears the seat which results inplay and consequently loss of sealing efilciency with the cylinder wall,and also with its seating groove. This is particularly disadvantageouswith respect to the top compression ring of the piston, which in orderto prevent blow-by should maintain a good seal in its seating groove andwith the cylinder wall at all times.

My invention is designed to overcome the I above-mentioned problems, andhas a its objects, among others, the provision of an improved pistonconstruction; in which a crown having an offset combustion cratertherein is so shaped as to distribute or dissipate heat evenly oruniformly to the periphery of the piston; means independent of a pistonbody and of relatively hard material is employed to provide a wearresistant seat for a piston ring and which is so mounted in the pistonbody as to have a certain degree of freerespect to the axis of thepiston to receive hot air and partially ignited fuel which are dis-=-charged from an auxiliary combustion chamber in the head of an engine,also offset with respect to the axis of the piston, for the reasonspreviously explained. As a result oi the offset or eccentric location ofthe crater in the piston crown, one peripheral part of the piston iscloser to the crater than the opposite peripheral part of the piston;and as a result, the closest peripheral part tends to become hotter thanthe opposite peripheral part. To cooperate in equalizing flow of heat tothe periphery of the piston, so as to have the entire periphery of thepiston adiacent the crown of substantially equal temperature and therebyminimize distortion of the crown portion of the piston whenit expands orcontracts resulting from change in temperature, the sectional thicknessof the wall of the crown is tapered between the peripheral part of thepiston closest to the combustion crater and the peripheral part oppositethereto, with the narrow portion of such wall thickness adjacent theperipheral part of the piston closest to the crater.

The taper or non-uniform thickness of the wall of the crown isaccomplished by having the under-surface of the wall of the crownspherically shaped and concentrically arranged with respect to the axisof the piston, to thereby be symmetrical with respect to such axis. Thethickness of the piston wall adjacent the periphery of suchunder-surface to the periphery of the piston is made substantially thesame all the way around, and the distance between the periphery of theunder-surface and the top of thepiston is also substantially the sameall the way around.

As a result of the described crown construction, the narrow portion ofthe wall of the crown serves to restrict or throttle the flow of heatto'that peripheral part of the piston closest to the combustion craterand unequal bowing of the top of I the piston is substantiallyeliminated to thus minimize distortion of each of the piston rings froma transverse plane at a right angle to the axis of the piston;particularly the top compression ring which is most important forminimizing blow-by. Hence, sealing cmciency of the rings with thecylinder wall and in their seating grooves is enhanced.

The piston body proper is preferably of a light metal of high heatconductivity, such as aluminum, for the reasons previousiy explained;and to preclude a harder metal piston ring from wearing into the softerbody of the piston and thereby develop excessive play which woulddestroy the sealing emciency of the piston ring in its seating grooveand with respect to the cylinder wall, I provide an independent hardmetal wear resistant ring groove band for mounting of the piston ring.Such bandrnay be provided for all of the upper piston rings but in thepreferred construction, I provide it for only the top com pressionpiston ring which is the ring located closest to the crown andconsequently subject to greatest distortion. Preferably, the ring grooveband is free of molecular union with the body of the piston as it is notcast integral there= aeoaare with or otherwise molecularly secured tosuch body, but is removably but firmly attached to the piston body bysuitable securing means. Although it is iirmly held, it has a certainlimited degree of freedom of movement by virtue of its non-molecularunion with the piston body which is advantageous because the band willnot follow all piston distortions resulting from changes in temperaturethereof; and this cooperates in maintaining proper seating of a pistonring in the band groove therefor and also alinement of such piston ringwith respect to a cylinder wall.

For retaining the ring groove band on the body of the piston, a securingring may be shrunk on such body over the band, but I prefer to employ athreaded securing ring having a screw connec tion with the peripheralpart of the piston crown, as this allows application of correct degreeof pressure on the ring groove band for holding it.

Reference is now made to the drawings for a more detailed description ofthe invention in which:

Fig. 1 is a fragmentary vertical sectional view, partly in elevation, ofthe piston of my invention mounted in an engine; portions of the head ofsuch engine being shown schematically.

Fig. 2 is a fragmentary enlarged sectional view of the piston of myinvention, illustrating the mounting of the ring groove band.

Fig. 3 is a vertical sectional view of the piston of my invention.

Fig. 4 is a vertical sectional elevation of such piston; with thesection taken in a plane indicated by line l'd in Fig. 3. i

Fig. 5 is an underneath sectional elevation of the crown portion of thepiston of my invention, taken in planes indicated by line 5-5 in Fig. 3.

Fig. 6 is a top view of the piston taken in a plane indicated by line6-S in Fig. 3.

Fig. 7 is avertical sectional elevation of a modified form of pistonconstruction.

With particular reference to Figs. 1 and 6, the piston of my inventioncomprises body 2, preferably of a metal *having a relatively high heatconductivity such as aluminum, and which isformed with combustionicrater 3 in the crown thereof, in the form or a segment of a sphere.

Such spherically shaped crater is offset or eccentrically disposed withrespect to the piston axis A; and by virtue of its oflfset relationshipthe piston is particularly adapted for employment in a compressionignition engine having an aux- I to allow room for valves 5 and adequatecooling jacket space in the head i of the engine. During the combustionphase, fuel is injected into precombustion chamber 4 from orifice 3 offuel injection nozzle 8; and from the precombnstion chamber partiallyignited fuel and hot combustion air are discharged through orifice itinto combustion crater 3. In Fig. l, the piston is shown in cylinder 32of the engine, which is preferably in the form of a removable liner.

Because of the offset relatiomhip of combustion crater 3, it will beapparent from Figs. 1, 3 and '5 that such crater lies closer toperipheral part l3 to expand more which would result in uneven movementof the piston ring mounting or peripheral belt portion it? of thepiston: particularly forming the under surface is of wall [3substantially symmetrical with respect to axis A of the adjacent the topcompreseral ring groove 33 formed in the band. Such band 32 is made ofrelatively hard metal, such as I cast iron,-to provide a wear resistantseat for the tially beyond the peripheral face of thepiston piston. Suchunder surface 19 is substantially spherical, the radius of curvature ofwhich is from a center on the axis of the piston designated by point P.The radius-of curvature of the sphericalcombustion chamber 3 is from acenter designated by point P' offset with respect to the axis of thepiston. Consequently, wall I8 is tapered between the peripheral parts i3and M of the piston, with the narrow portion 2| of wall 13 adjacentperipheral part l3 which tends to become hottest. As a result, flow ofheat'is choked or throttled to such' peripheral part I3 to cooperate inequalizing flow of heat. The thickness of narrow portion 2| .of wall l3and the degree of taper of wall ID will determine the extent to whichsuch narrow portion throttles the flow of heat. By choosing. the propervertical and transverse distances between points P and P, the correctdegree of taper of wall I 3 and the proper thickness of narrow wallportion 2!, may be readily obtained for any given size piston. Becauseof the substantially symmetrical shape of the under-surface IQ of thewall l8 of the-piston crown, a substantially uniform wall thickness Tobtains from adjacent the periphery of undersuriace l9 to the peripheryof the piston; and

the periphery of under-surface I3 is substantially the same distance Dall the way around, from the top surface of the crown of the piston.This is also important in obtaining substantial equal expansion andcontraction of the tion of the piston adjacent the crown. to obviatedistortion.

The described shape of the crown wall l8 of the piston may be employedalone in any type of piston having an offset combustion crater in itscrown, and made of any suitable material. to perform the describedfunction of equalizing flow of heat to minimize distortion. However,since the preferred piston in which my invention is employed is made ofaluminum, for the reasons previously explained, in which harder metalpiston rings would wear in their seating grooves. and thus develop playwith consequent loss of sealing efficiency, I preferably also employ'insuch piston a special mounting for at least the important topcompression ring toobviate such development of play and cooperate withthe special crown wall construction of my invention in maintainingproper alinement thereof with respect to the cylinder wall.

For this purpose, the top peripheral portion'of the piston is formedwith peripheral recess 30 which provides peripheral shoulder 3| forsupporting an independent one piece or integral, unbroken piston ringgroove band 32 in recess 33, and which fits with slight radial clearance32' at its inside; the inside radial clearance precludperipheral poringbinding of the band against the body of the.

piston when the parts of the piston expand under operating temperaturesto which the piston may be subjected. As a result, such arrangementcooperates in maintaining eflicacious sealing relationship of the pistonring l1, seated in periphpiston ring in ring groove 33. Band 32 does notserve in the capacity of a packing or sealing ring,

. as such function is accomplished by piston ring 11; and in thisconnection, it will be noted that because the band 32 is integral andunbroken, it-

is non-Felastic radially. Furthermore, the peripheral face of the band32 does not project substanbody but is substantially coextensive withsuch piston body face. Preferably, the under surface 34 of suchband andshoulder 3| lie in a plane extending at a right angle to the axis of thepiston and the upper surface 36 of the band is inclined to provide acompensating feature, which are described more fully, and claimed in myPatent No. 2,349.919 issued May 30, 1944, for Fitting of members. Also,the top side of piston ring groove 33 in band 32 is preferably formedwith an annular blow-by minimizing channel 33, the

purpose of which is more fully described, and claimed in my Patent No.2,349,918 issued May 30. 1944, for Piston construction."

I preferably firmly retain ring groove band 32 in position by means ofinternally threaded securing ring or nut 39 of any suitable material,

such as aluminum, having a screw connection in recess 30 with body 2 ofthe piston. By turning securing ring 39 the correct number of turns, theproper degree of pressure may be applied to hold or clamp ring grooveband 32 firmly in position; and because of such firm holding of theband, it cannot rotate about the axis of the piston. To preventrotational movement of securing ring 39 after it is once screwed ontothe piston the proper extent, I preferably provide diametricallyopposite tapered pins ll (Fig. 4) which pass transversely throughsuitable apertures formed in the securingring and into recesses 42formed in the body of the piston. Only one pin 4| may be employed if sodesired. Preferably, the underside of securing ring 33, adjacent band32. is formed with a peripheral notch or recess 43 so as to avoidapplication of pressure directly over the outer peripheral portion ofring groove band 32, and hence obviate pinching of the piston ring whichwould result in undesirable distortion thereof will resist wearresulting from forces which tend to move a piston ring therein, whichforces always obtain during operation of a piston in an engine. Hence.play between the piston ring and its seating groove 33 is minimized; andthe piston ring will not only remain in good sealing relationship withits groove but it will also be maintained in proper sealing alinem'entwith respect to the cylinder wall. Ring groove band 32 may be made ofsufiicient depth to support more than one piston ring. but I find thatfor minimizing blow-by in a cylinder, the top compression ring is theimportant factor. Hence in the preferred construction. I only employ theindependent ring groove band 32 for the top compression ring I! which ismounted therein.

It is to be noted-from the preceding description that although ringgroove band32 is rigid and firmly held in position, it is free ofmolecular union with the body of the piston since it is not attached tosuch body or otherwise molecularly secured thereto by welding 'or othermeans. .Asa result, the baud tends to have a certain limited degree offreedom of movement, which is enacoaaie because the band will not followall distortions of the piston crown; and this feature alone helps tomaintain proper 'alinement of a piston ring in the band, with respect toa cylinder wall, and also proper sealing of such ring in its seatinggroove.

Consequently, the independent ring groove band, irrespective of whetherit is of'harder material than a piston ring adapted to be mountedtherein, or of different material than a piston body, has utility alonewhen employed in any lrind of piston.

The special preferred shape of ring groove band 32 and the blow-byminimizing channel 38 therein are desirable for the purposes explainedin my patents to which I have previously referred. However, in so far asproviding the constructional feature of a wear resistant seat for apiston ring mounted therein, is concerned, the ring groove band may bemade flat or any other suitable shape as long ash; is of hard metalsuficient to resist wear of a piston ring therein, and it need not beformed with a blow-by minimizing channel. Also, any other suitable meansmay be employed to hold such ring groove band in position. In Fig. '7, Ihave illustrated a modified form of construction in which the ringgroove band as is provided with perfectly fiat top and bottom surfacesextending at a right angle with respect to the axis of the piston; andit is held in position by means of securing ring it shrunk on the pistonbody. Such construction, irrespective of the material of ring grooveband as, will also provide the advantage resulting from the limitedfreedom of movement of the band. i

The special constructional mounting of my invention for piston rings,may be employed in any type of piston formed with or without a crater.However, in the particular piston wherein my invention is employed andwhich has the ofifset combustion crater, both the special shape of thepiston crown and the special ring mounting are desirable as they bothcooperate in minimizing misalinement of a piston ring, particularly thetop compression ring, with respect to a cylinder wall, and theycooperate to maintain proper sealing of said ring in its seating groove.

I, therefore, claim as my invention:

1. A piston of the type in which the crown thereof is provided with arecess forming a combustion crater ofiset with respect to the axis ofthe piston, whereby the peripheral part oi the piston closest to thecrater tends to become hotterthan the opposite Peripheral part of thepiston, the periphery of the piston adjacent the crown having a pistonsealing ring seating groove therein, a ring in said groove, theunder-surface of the wall of said crown being convex, and the crosssection of said wall gradually increasing in 7 thicknes between saidperipheral parts with the 2. A piston of the type in which the crownthereof is provided with a recess forming a substantially sphericalcombustion crater offset with respect to the axis of the piston, wherebythe peripheral part of the piston closest to the crater tends to becomehotter than the opposite peripheral part of the piston, the periphery ofthe piston'adjacent the crown having a piston sealing ring seatinggroove therein, a ring in said groove, the under-surface of the wall ofsaid crown being convex and of substantially spherical contoursubstantially symmetrical with respect to the axis of the piston,'andthe cross section of said wall gradually increasing in thickness betweensaid peripheral parts with the narrow portion thereof adjacent saidfirst mentioned peripheral part, to throttle flow of heat thereto andthus substantially equalize said fiQW of heat to such peripheralpartaWhereby misalinemeht of said piston ring which might otherwiseoccur from unequal heat distribution is minimized.

3. A piston of the type in which the crown thereof is provided with arecess forming a substantially spherical combustionncrater the center ofthe radius of curvature of which is onset relative to the piston axis,whereby the crater is offset with respect to such axis and the pcnarrowportion thereof adjacent said first menripheral part of the-pistonclosest to the crater tends to become hotter than the oppositeperipheral part of the piston', the periphery of the piston adjacent thecrown having a piston seal ing ring seating groove therein, a ring insaid groove, the under-surface of the wall of said crown being convexand of substantially spherical contour the center of the radius ofcurvature of which is substantially on the piston axis whereby suchunder-surface is symmetrical with respect to said axis, the wallthickness or? the.

piston being substantially uniform from adjacent the periphery of saidunder-surface to the periphery of the piston, the periphery of saidundeli-surface being substantially the same distance all the way aroundfrom the top surface of the piston crown, and the cross section of saidcrown wall gradually increasing in thickness between said peripheralparts with the narrow portion thereof adjacent said first mentionedperipheral part, to throttle flow of heat theretoand thussubstantiallyequalize said fiow of heat to such peripheral parts, wherebymisalinement of said piston ring which might otherwise occur fromunequal heat distribution is minimized.

e. A piston having a crown with a convex un-- dersur face ofsubstantially spherical contour,

the center of t e radius of curvature of which is coincidental wi h thepiston axis, and having a combustion crater in its upper surface ofsubstantially spherical contour, the center of the radius of curvatureof which is oiiset from the piston axis to provide a crown wall ofunequal thickness for controlling the distribution of heat from thecombustion crater to the periphery of the piston.

OSCAR L. STARR.

